Electronic control switch



Aug. 19, 1958 H, CUTLER 2,848,659

ELECTRONIC CONTROL SWITCH Filed June 10, 1955 in Men t 02'":

lean f7. Cari/en HAS A t t orvvgg United States Patent ELECTRONICCONTROL SWITCH Leon H. Cutler, Milford, Conn, assignor to GeneralElectric Company, a corporation of New York Application June 10, 1955,Serial No. 514,659

5 Claims. (Cl. 317149) This invention relates to an electric circuitcontrol switch operable by touch contact; more particularly, it relatesto an electric switch operable by touch contact with a pair of touchsurfaces which provides reliable operation under a wide variety ofexternal conditions.

In Harnden et al. application S. N. 497,242, filed March 28, 1955, whichis assigned to the same assignee as the present application, there isdescribed an electronically controlled switch in which a glow tubebecomes conducting to energize a latching relay upon contact of a personwith a touch surface. The present invention is directed to a switch ofthe same general type as that disclosed in the Harnden et a1.application. This invention is directed particularly toward additionalcircuit elements which confer greater reliability of operation upon theswitch.

It is an object of the present invention to provide an electronic typecircuit switch operable by touch contact which will operate reliablyunder almost all operating conditions to which the switch is likely tobe subjected.

It is another object of the invention to provide a switch operable bytouch contact wherein there are two touch areas, one of which serves asa ground plane.

It is a further object of the invention to provide a switch operable bytouch contact wherein the dark sensitivity of an electronic element isprevented.

A further object of the invention is to provide an electronic switchwhich avoids the buildup of a charge on circuit elements therebypreventing spurious operation.

Other objects of the invention will become apparent from the followingspecification considered in conjunction with the appended drawing whichis a diagrammatic view of the circuit whereby the switch of the presentinvention operates.

Briefly stated, in accordance with one of its embodiments, the presentinvention comprises a switch operable by touch contact in which there isa glow tube having at least three electrodes, one of which is a controlelectrode, one a cathode, and one an anode; a latching relay havingcontacts which alternately open and close an external circuit uponenergization of the relay; a capacitor in a circuit connecting the tubeand relay in series and the capacitor in parallel therewith; a source oflight in proximity to the glow tube; a first touch surface connected tothe relay-tube-capacitor circuit at the potential of the anode side ofthe alternating current input; a second touch surface; and a highresistance circuit connecting the second touch surface to the controlelectrode of the glow tube, the circuit including high resistancebranchconnections to the other two electrodes of the glow tube.

The switch illustrated diagrammatically in the drawing is intended tooperate on alternating current of the normal 110-120 volt range and,therefore, the circuit is shown connected to a conventional plugalthough such a plug is not necessarily a part of the switch mechanismitself. Half-wave rectification of the line voltage is achieved by meansof a rectifier 20 which may be of the conventional selenium type, butother types are also satis- EQQ factory. The line voltage is utilized tocharge a capacitor 11, which is preferably of the electrolytic type,through a resistor 23. The capacitor 11 is connected across a circuitcomprising a miniature glow tube 12 and a latching relay 13 whichalternately opens and closes an external circuit 14 upon energization.The resistor 23 limits the rate of charging of the capacitor 11 to asafe value and, together with the capacitor, determines the retiringtime in addition to which it limits current flow from the supply throughthe relay 13 and tube 12 when the capacitor 11 discharges.

The miniature glow tube 12 preferably has at least three elementsconsisting of a control electrode 15, a cathode 15a, and an anode 15b.The tube 12 is desirably a miniature neon tube having in the envelopethree electrodes of the same configuration with the control electrode 1Soccupying an intermediate position which completely interrupts the lineof sight between the cathode 15a and anode 15b. The three electrodes canbe composed of metallic rod material about a quarter-inch in length byabout one thirty-second-inch in width. Normally, the few milliamperecurrent-carrying capacity of the tube 12 is much too small to energize arelay. However, the tube may be overloaded sufficiently (i. e. 200 ma.)for a short interval to bring about momentary energization of a relay.Since the relay 13 is of the latching type, momentary energizationthereof is sufficient to reverse the setting of its contacts.

The latching relay 13 has an armature 17 which is not a part of theexternal electrical circuit 14 but, nevertheless, eifectuates themechanical movement which controls the circuit. The actual circuitcompleting members are an immovable element 18 and a pair of springbiased elements 19 and 21, the elements 18 and 19 being equipped withcontacting buttons 13a and 19a respectively.

The elements 19 and 21, which are biased in the direction of each other,have cooperating step-shaped ends whereby, in the open-contact positionillustrated, the element 21 holds the element 19 out of contact with theelement 18. The element 21 is equipped with a detent 22 which isengageable by the end of the attracted armature 17 when the contacts arein the open position illustrated. After engaging the detent 22, armaturemovement forces the element 21 out of engagement with the element 19which brings into engagement the contacts 18a and 1% due to the springbias of the element 19. At the same time, the tip of the element 15engages the element 21 to hold the detent 22 out of the path of travelof the armature 17. On the next energization of the relay 13, the tripportion of the armature 17 misses the detent 22 and engages the element19 to open the contacts and 19a and enable the element 22 to spring intolocking position and maintain the contacts in open position. Other typesof latching relay are available and may be substituted for theparticular type illustrated.

A control circuit for the tube 12 consists of a touch surface or plate16 connected to the control electrode 15 through a trunk resistor 27. Abranch circuit connects the touch plate 16 to the cathode 15a throughthe branch resistor 29 which preferably, though not necessarily, has astabilizing capacitor 31 in circuit therewith. The anode 15b isconnected to the touch surface 16 through a branch circuit including aresistor 28.

It is desirable that in addition to the touch surface 16 there beanother touch surface 25-preferably in spaced relation theretoto providethrough a resistor 26 an electrical coupling to the anode of the tube 12thereby avoiding the necessity of having the plug 10 always connectedfor the same polarity. In addition, by

coupling the touch surface 25 to the anode side of the source, theeffect of the capacitance to ground of the person contacting the touchsurface is no longer required and it is the conductivity (or impedance)of a person bridging the touch surfaces 16 and 25 which raises thepotential of the control electrode 15 toward the anode 15b to render thetube 12 conducting. This, in etfcct, provides an artificial internalground plane.

The tube 12 has a tendency to alter its characteristics in an erraticmanner according to whether it is surrounded by light or darkness. Sincethis can result in spurious operation of the switch, a source of light32 is connected across the line through a resistor 33. Since the sourceof light is always in operation, it is desirable that it be placed closeto the tube 12 and operate on very low current. A miniature neon tube issatisfactory for this purpose both from the standpoint of initial cost,reliability, and low power consumption.

Spurious conduction of the tube 12 due to the gradual accumulation of astatic charge on the surface 16 is avoided due to the fact that thebranch circuits through the resistors 28 and 29 and capacitor 31 drainoff such charge.

In operating the switch illustrated, the circuit is connected to asource of energy which charges the capacitor 11. The circuitcharacteristics are such that breakdown voltage of the tube 12 is notattained. When a person now touches the surfaces 16 and 25, anodepotential is applied to the control electrode 15 to enable the tube 12to become momentarily conducting, thereby energizing the relay 13 tochange the setting of its contacts either to open or to close thecircuit 14. While the external circuit 14 has not been shown in itsentirety, it is obvious that any switch control function such as turninga lamp on and off or starting and stopping an electric motor orelectronic apparatus could be brought about by the switch circuitillustrated. The touch surfaces 16 and 25 do not have to have anyparticular configuration, but in most applications it is desirable thatthey be placed close to each other, as by interleaving, so that it isdifficult to touch one without also touching the other. There is thusprovided a switch which is particularly useful for persons who have lostthe use of their fingers since mere contact of the touch surfaces 16 and25 with the arm or any part of the body will effect operation of theswitch.

It is obvious that the circuit elements may be correlated for operationunder widely varying voltage conditions. Such correlation of circuitcomponents is within the realm of those skilled in the art and,therefore, the following listing of values for the resistors andcapacitors of the circuit is intended to be illustrative without beinglimiting. The elements are identified by the numbers shown on thedrawing.

Resistors Number Resistance (megohms) 23 0.0082 26 0.68 27 0.1 28 29 6.833 0.47

Capacitors Number: Capacitance 11 mfd 40 31 mmfd 700 While the inventionhas been discussed primarily with reference to the specific embodimentillustrated, there are many obvious modifications which fall within thespirit of the invention. Therefore, the invention is limited in scopeonly as may be necessitated by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is: t

l. A switch operable by touch contact comprising: a first glow tubehaving an anode, cathode, and control electrode; a latching relayconnected to the cathode of said tube, said relay having. contactsadapted to control an external circuit; means for connecting the circuitformed by said tube and relay to a source of electrical energy; acapacitor connected across said tube and relay circuit; a second glowtube positioned to radiate light on said first glow tube; a first touchsurface of conducting material connected through a high resistance tothe anode of said first glow tube; and a second touch surface ofconducting material in spaced relation with said first touch surface,said second touch surface being connected to all of the electrodes ofsaid first glow tube through a branching circuit including a trunkresistor and additional resistors in the branch circuits leading to thecathode and anode, whereby touch contact with said touch surfaceseffects conduction through said first glow tube when said switch isconnected to a source of electrical potential- 2. A switch operable bytouch contact comprising: a glow tube having an anode, cathode, andcontrol electrode; a latching relay energizable by a circuit throughsaid glow tube; a capacitor to control the output from said glow tube tosaid relay; a source of light to radiate light on said glow tube; afirst touch surface of conducting material connected as a ground planefor said switch; a second touch surface of conducting material in spacedrelation to said first touch surface; and a circuit including a trunkresistor connecting said second touch surface to the control electrodeof said glow tube, said circuit also including high resistance branchconnections to the other two electrodes of said glow tube.

3. A switch operable by touch contact comprising: a glow tube having atleast three electrodes one of which is a control electrode, one acathode and one an anode; a latching relay having contacts whichalternately open and close an external circuit upon energization of saidrelay; a capacitor; a circuit connecting said tube and relay in seriesand said capacitor in shunt of said tube and relay, whereby the chargeupon said capacitor controls the output from said glow tube to saidrelay; a source of light to radiate light on said glow tube; a firsttouch surface connected to the anode of said tube at ground potential; asecond touch surface; and a high resistance circuit connecting saidsecond touch surface to the control electrode of said glow tube, saidcircuit including high resistance branch connections to the other twoelectrodes of said glow tube, whereby said glow tube becomes conductingto energize said relay when said switch is connected to a source ofelectrical energy and said touch surfaces are bridged by touch contact.

4. A switch operable by touch contact as claimed in claim 3 whereinthere is means for rectifying an altermating current input to thecapacitor-glow tube-relay circuit.

5. A switch operable by touch contact as claimed in claim 3 whereinthere is a capacitor connected in parallel in the branch circuit leadingfrom the second touch surface to the cathode of the glow tube.

References Cited in the file of this patent UNITED STATES PATENTS 1 ,5 35, 3 60

